An autonomous vehicle, such as a mobile robot, typically comprises some type of sensor system for sensing an environment through which the vehicle navigates. Preferably, the sensor system has the capability to detect obstacles within the path of the robot so that appropriate action may be taken. This action may include altering the path of the robot in order to steer around the obstacle. Alternatively, a sensed object may represent a navigation landmark, such as a support post, door frame, or wall, which the robot uses as a registration reference in following a preprogrammed trajectory. Systems employing ultrasonic detectors, mechanical contact devices and laser ranging apparatus are known in the art. Other systems which include a camera to observe the environment and a passive image processing system are also known.
A problem associated with ultrasonic detectors relates to the difficulty in obtaining reliable and consistent range signals in an environment which normally includes a number of objects having differing specular reflection characteristics. The objects also typically differ in size, surface characteristics and orientation relative to the ultrasound transmitter. A problem associated with mechanical contact devices relates at least to a lack of resolution and to a requirement that the obstacle actually be contacted in order to generate a signal. For some applications, such as navigation through a workplace or a hospital, the obstacle may be a human being. As can be appreciated, for these applications physical contact with the obstacle may be undesirable. Laser ranging systems are expensive, bulky, and consume substantial power. Traditional passive scene analysis vision systems require large amounts of computing power, are relatively slow and often yield erroneous results. Typically the interpretation of data is too slow to be useful for real time navigation, and may prove erroneous, such as interpreting a shadow as an object, which results in navigation errors.
It has also been known to provide visual markers or "beacons" within the robot's environment. Such beacons are undesirable in that they introduce additional cost and complexity to the system and constrain the motion of the robot to a region wherein the beacons are visible.
Commercial applications of mobile robots in the service sector include floor cleaning, aids to the handicapped, hospital delivery systems, mail carts, and security. These applications require robust, reliable navigation using sensors which are low in cost and power consumption while providing real-time maneuvering data.
It is therefor one object of the invention to provide a simplification of vision and vision processing for a mobile robot.
It is another object of the invention to provide a vision system for a mobile robot, the system requiring a minimum of image processing complexity while yet having an image resolution which is sufficient for guiding the robot through an environment.
It is a further object of the invention to provide a vision system for a mobile robot which does not require beacons or other environmental modification means to be disposed within the robot's environment.
It is another object of the invention to provide a vision system for a mobile robot which provides a complete and unambiguous interpretation of obstacles and landmarks relevant to navigation which lie in the path of the robot while having a minimal complexity, cost and power consumption as compared to conventional passive image analysis systems.
It is one still further object of the invention to provide a vision system for a mobile robot which operates in a high speed manner and which permits the continuous, adaptive motion of the robot through the robot's environment.